Dear Readers, I have been thoroughly enjoying this series of virtual meetings organised by the London Natural History Society – they have been varied, interesting and have introduced me to lots of new facts and ways of looking at the natural world. This talk was no exception – Professor Duckett’s main interests are bryophytes (liverworts and mosses) and he has been studying them for decades. In this talk, he was particularly interested in the effects of air pollution and climate change on London’s plants, especially those that grow on Hampstead Heath, which has been one of his main study areas.
Professor Duckett saw the seminal events of the last 50 years as being:
- the Clean Air Acts of 1956 and 1968, which led to a dramatic fall in Sulphur Dioxide and soot pollution
- The rising levels of Nitrous Oxide pollution from car exhausts
- Climate change
The effects of these three changes were woven through his talk, but first he set the scene. The forest on Hampstead Heath is, like my local Coldfall Wood, ancient woodland with hornbeam coppice and oak standards. This meant that the hornbeams (incidentally the very last of our native trees to arrive before rising sea levels cut the UK off from the rest of Europe about 12,000 years ago) were cut for firewood every few years, while the oaks were left to grow for up to a hundred years before being cut. He estimated that the oldest oaks in the wood were probably about 400 years old, but interestingly the coppiced hornbeams could be older. Some of them were last coppiced as recently as ninety years ago.
The wood itself is probably 6000 to 7000 years old, part of a much larger wood that covered most of this part of the world. Professor Duckett makes the point that a mature tree captures up to 50lbs of carbon every year, while a sapling captures only .1lb. When you hear developers talking about replacing the mature woods that they plan to cut down with saplings, it’s worth noting that this is not a like-for-like replacement, as if we didn’t already guess that this was the case.
The oaks on Hampstead Heath are both Sessile Oaks (Quercus petraea) and English Oaks (Quercus robur) and Professor Duckett points out that there are also many hybrids between the two in the wood. There are also an increasing number of Turkey Oaks (Quercus cerris) which was introduced as an ornamental tree in the Eighteenth Century, and some evergreen Holm Oaks (Quercus ilex) – long-time readers might remember a pair of these trees growing outside Mum and Dad’s care home in Dorset.
Incidentally, you can tell the acorns of the turkey oak because they have hairy caps! Who knew…
Another common plant on the Heath is Alder Buckthorn (Frangula alnus). Professor Duckett told us that this was the foodplant of the Brimstone butterfly (Gonepteryx rhamni), and he described it as ‘unfortunately not endangered’, for reasons that will become apparent. The butterfly is in fact doing very well as the climate warms, and is moving north at a rate of knots.
English Heritage have the responsibility to ‘restore and maintain the original landscape’ of the Kenwood Estate (which constitutes an important part of the Heath) whilst maintaining biodiversity. Alas, Professor Duckett points out that a large stand of Alder Buckthorn which wasn’t in Repton’s original design is going to be destroyed, because the brimstone is doing very well. It must sometimes feel as if a species is damned if it’s doing badly, but also damned if it’s increasing in numbers.
Interestingly, although Professor Duckett sees a number of dangers to the wood itself (from ash dieback, from competition from non-native trees such as the Turkey Oak and Norway Maple, and from climate change), he sees the biggest conservation priority in the wood as being….the bog.
At this point, my head swivelled. Bogs are vanishingly rare in London, and I had no idea that Hampstead had one At All. However, sphagnum moss was first recorded in 1877, and there used to be not one but three bogs. The other two are gone, and one remains. This one is a valley bog, where nutrient-poor water drains into a decline, and it used to be much more species-rich – sundew used to grow here, for example. This insectivorous plant exudes drops of a sticky liquid that catch little flies to provide the plant with the nutrients that are missing from the soil.
The bog had been getting rather overgrown with brambles and shrub, but this year a socially-distanced team of volunteers have been clearing the area, and the sphagnum is already regenerating, along with the largest moss in the UK, Polytrichum commune.
Finally, Professor Duckett returned to his theme of air pollution. The sulphur dioxide in the air from coal-burning during the early twentieth century rendered London a virtual lichen desert – by the time of the Clean Air Acts in 1956 and 1968, there was only one species of lichen left in the whole capital. After this, however, species gradually came back – today, you can see almost 150 species of lichen on Hampstead Heath.
Furthermore, although the Nitrous Oxide pollution along our main roads is bad for most living things, it provides nutrients for nitrogen-loving bryophytes, who can be seen growing on the trees along our main roads. One of these is Syntrichia papillosa or Marble Screw-moss, an urban species which is thriving in the low-sulphur, high nitrogen air.
Finally, climate change is improving the conditions for some plants, such as the Mediterranean Liverwort, which used to only live in Cornwall in 1966, and now lives as far afield as the Western Isles of Scotland.
Professor Duckett’s final worry, though, was the lack of botanists being trained up in the UK. He has spent the past five decades studying mosses and liverworts, and has been able to follow the rise and fall of various species. During this time, fewer and fewer universities have been offering courses on botany (or on zoology either). How are we going to monitor what’s going on in our ecosystems if no one is trained? Let’s hope that the generation of citizen scientists who have become involved over the past few years can fill some of the gap.
If you would like to watch the whole talk (and the very interesting discussion that came afterwards) have a look here.
Photo One by Franz Xaver, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons
Photo Two by Sten Porse, CC BY-SA 3.0 , via Wikimedia Commons
Photo Three by By Charles J Sharp – Own work, from Sharp Photography, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=38298003
Photo Four By No machine-readable author provided. Migas assumed (based on copyright claims). – No machine-readable source provided. Own work assumed (based on copyright claims)., CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=419620
Photo Five by ceridwen / Common haircap moss (Polytrichum commune)
Photo Six by HermannSchachner, CC0, via Wikimedia Commons
Photo Seven from http://www.dorsetnature.co.uk/pages-liv/lv-02.html